To originate a voice over IP (VoIP) call between a calling device and a called device in an IMS network, an originating Serving Call Session Control Function (S-CSCF) that serves the calling device must generate at least two database queries to connect the call. In a first query, the originating S-CSCF submits an E.164 number of the called device to a tElephone NUmber Mapping (ENUM) system which performs a first database search to identify a SIP URI of the called device. The ENUM provides the SIP URI of the called device to the originating S-CSCF in response to the first query.
In a second query, the originating S-CSCF then submits the received SIP URI to an Interrogating CSCF (I-CSCF) to identify a terminating S-CSCF serving the called device. The I-CSCF forwards the SIP URI to a Home Subscriber Server (HSS) to perform a second database search for the second S-CSCF. The HSS provides to the I-CSCF a SIP URI of the terminating S-CSCF in response to the second query. Upon performing the two database queries, the terminating S-CSCF contacts a corresponding Proxy-CSCF serving the called device to place the call.
The SIP URI of the terminating S-CSCF is recorded in a database of the HSS during registration of an IMS communication device. Registration of IMS devices thus adds to the number of database transactions taking place at the HSS.
Performing multiple database queries and recordings at the HSS during registrations and call originations increases the HSS's workload and thereby introduces cost and potential maintenance issues for a service provider of the IMS network. Similar issues arise when IMS calls are made between IMS networks managed by independent IMS operators.